We have demonstrated that the 60 kD protein previously characterized on a subset of T lymphocytes and named "T4", is another example of shared components between the brain and immune system. Thus, we have demonstrated that this cell surface molecule can be cross-linked to 125I labeled AIDS virus envelope and immunoprecipitated by the Mab OKT4 in both T cells and brain. Our work shows that the neuropsychiatric effects of AIDS may not, as previously thought, be due to inflammatory processes but due to a direct neuronal infection of the virus. Gp120 was shown to be the most toxic neuronal substance known. Gp120, VIP and Peptide T all compete for binding to the Ty receptor. Gp120 apparently blocks VIP attachment. Apparently the hormone VIP needed for the maintenance of a healthy cell, is replaced by Peptide T which displaces Gp120. Peptide T and other homologs can block Gp120 killing effects on neuronal survival at 10-12m. Peptide T and several rationally designed peptide analogs appear to bind with high affinity to the AIDS virus receptor, blocking viral infectivity at very low concentrations. We expect that synthetic peptide heteropolymers employing this core pentapeptide attachment sequence will provide valuable as an approach for a vaccine for AIDS. This method and approach appears useful for exploring the presence of other virus receptors in the brain. For example, we have already observed that the Epstein- Barr virus which has been known to use the complement receptor on B cells as a receptor entry protein, may actually infect brain via the same receptor molecule which we have recently identified in brain.